The invention relates generally to the field of polymer chemistry. More particularly, the invention relates to metathesis of functionalized allylic olefins.
Olefin metathesis is a reaction commonly employed in polymer chemistry. In this reaction, the carbon-carbon double bonds present in a starting olefin molecule (substrate) are broken, and the molecule is rearranged into a new olefin molecule (product). Several varieties of olefin metathesis are known including acyclic diene metathesis (ADMET), ring-opening metathesis polymerization (ROMP), and ring-closing metathesis polymerization (RCM). The basic mechanism for each of these processes is thought to involve a cycloaddition reaction between the starting olefin molecule and a transition metal alkylidene complex that causes the formation of an intermediate metallacyclobutane. The intermediate metallacyclobutane breaks up to form the new olefin molecule and a new alkylidene.
Several generations of catalysts have been developed for olefin metathesis reactions. Among these, so-called xe2x80x9cBlack Boxxe2x80x9d catalysts consist of a high valent transition metal halide (or oxide or halo-oxide) together with an alkylating component such as alkyl aluminum or alkyl zinc. Other metathesis cataylsts include: titanocene-based catalysts; Schrock""s tungsten (W), molybdenum (Mo), and rhenium (Re) catalysts; and Grubbs"" ruthenium (Ru) catalysts (e.g., compound (1) shown below). 
Each of the foregoing catalysts has certain advantages and disadvantages that make each more suited for some applications, but less suited for others. For example, Black Box catalysts are known to have a very low tolerance for functional groups, while Schrock""s catalysts have a higher tolerance for functional groups but are sensitive to air and moisture.
Although catalysts such as Schrock""s and Grubbs"" catalysts have been shown to exhibit tolerance for functional groups, even these have only limited catalytic activity in some reactions. For example, the foregoing catalysts show poor activity when olefins containing electron-rich functionalities are employed as substrates. Moreover, metathesis activity is substantially decreased or inhibited when a heteroatom is placed near the olefin site. See, e.g., Fxc3xcrstner, A., ed. In Alkene Metathesis in Organic Synthesis. Springer-Verlag: Berlin, 1998; Ivin and Mol, In Olefin Metathesis and Metathesis Polymerization, 2nd ed.; Academic: San Diego, 1997. Presumably, an alkylidene chelate complex (3) is formed between the metal and the olefin (2), deactivating the catalyst as shown below (Ln=an organic ligand; Ph=phenyl). 
This effect is most pronounced with respect to vinyl and allylic olefins. For example, Hoye has shown that RCM of allylic alcohols using Grubbs"" ruthenium catalyst (1) can require up to 1 equivalent of catalyst to efficiently promote the metathesis reaction. Hoye and Zhao, Org. Lett. 1999, 1, 1123. In addition, in some cases, these molecules are metathesis inactive when using either Grubbs"" ruthenium catalyst (1) or Schrock""s molybdenum catalyst. See, Schwab, et al., Angew. Chem. Int. Ed. Engl. 1995, 34, 2039; Schwab et al., J. Am. Chem. Soc. 1996, 118, 100; and Belderrain and Grubbs, Organometallics 1997, 16, 4001; Bazan et al., J. Am. Chem. Soc. 1991, 113, 6899; Bazan et al., J. Am. Chem. Soc. 1990, 112, 8378; Schrock et al., J. Am. Chem. Soc. 1990, 112, 3875; Schrock, R. R. Tetrahedron 1999, 55, 8141; and Schrock, R. R. Polyhedron 1995, 14, 3177).
These limitations of conventional olefin metathesis chemistry result in increased costs of several industrially useful feedstock chemicals such as functionalized monomers used to produce various polymers. Therefore, because the cost of allylic olefins is less than of alkenes containing distant functional groups, a metathesis-based method for producing such feedstock chemicals from allylic olefins is expected to reduce the overall costs of producing certain polymers. For example, a metathesis-based method of making 1,4-butanediol from allyl alcohol could reduce the costs of producing polybutylene terephthalate (PBT). Similarly, the ability to successfully condense other functionalized allyl olefins (e.g., allyl cyanide) would be useful to produce feedstock chemicals that could be used in the production of other polymers such as nylon 6,6.
The invention relates to the discovery of an improved method for making functionalized allylic olefins useful in the production of industrially important polymers. The method utilizes 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium benzylidene [Ru*] (4), the ruthenium-based metathesis catalyst shown below (Cy=cyclopentyl) that was recently developed by Grubbs and coworkers using imidazolium ligands. See, Scholl et al., Org. Lett. 1999, 1:953.
Using this catalyst, it has been shown for the first time that functionalized olefins such as allyl alcohol and allyl cyanide are efficiently and effectively converted to new olefin products by metathesis condensation. Consequently, the present invention should facilitate the synthesis of a broad range of molecules not previously producible via metathesis chemistry.
Accordingly, the invention features a method for condensing a functionalized allylic olefin substrate by metathesis chemistry. The method includes the steps of: (a) providing a functionalized allylic olefin substrate; (b) providing a ruthenium-based catalyst capable of catalyzing the metathesis condensation of the functionalized allylic olefin substrate; (c) contacting the functionalized allylic olefin substrate with the catalyst to form a reaction mixture; and (d) placing the reaction mixture under conditions that result in the formation of a functionalized olefin product via metathesis condensation, the functionalized olefin product having a different chemical structure than the functionalized allylic olefin substrate.
The catalyst used in this method can be 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium benzylidene (Ru*). The functionalized allylic olefin substrate can be functionalized with an electron rich functional group. For example, the functionalized allylic olefin substrate can be allyl alcohol or allyl cyanide. Where the functionalized allylic olefin substrate is allyl alcohol, the functionalized allylic olefin product can be 2-butene-1,4-diol. Where the functionalized allylic olefin substrate is allyl cyanide, the functionalized allylic olefin product can be 1,4-dicyanobutene.
The step of placing the reaction mixture under conditions that result in the formation of the functionalized olefin product via metathesis condensation can include placing the reaction mixture at a temperature of between about 10xc2x0 C. and 70xc2x0 C.; placing the reaction mixture at a temperature of about 23xc2x0 C. or less; placing the reaction mixture under about standard atmospheric pressure; applying a vacuum force to the reaction mixture; and/or placing the reaction mixture under an inert atmosphere (e.g., under N2 or Ar). This step can also be performed under anhydrous conditions. The substrate:catalyst ratio (mol:mol) used in this method can be between about 1:1 to 1000:1, and is preferably greater than about 10:1.
The method of the invention can further include a step (e) of hydrogenating the functionalized allylic olefin product. This hydrogenation step can be catalyzed using residue of the ruthenium-based catalyst formed during the step of placing the reaction mixture under conditions that result in the formation of a functionalized olefin product via metathesis condensation. In this aspect of the method of the invention, where the functionalized allylic olefin substrate is allyl alcohol and the functionalized allylic olefin product is 2-butene-1,4-diol, the step of hydrogenating the functionalized allylic olefin product can result in the production of butane-1,4-diol.
The invention also features a reaction mixture including a functionalized allylic olefin substrate; a ruthenium-based catalyst capable of catalyzing the metathesis condensation of the functionalized allylic olefin substrate; and a solvent, the solvent having dissolved therein the substrate and the catalyst. In this reaction mixture, the catalyst can be 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium benzylidene (Ru*); the functionalized allylic olefin substrate can be allyl alcohol and allyl cyanide; and the solvent can be a hydrocarbon-based solvent such as dichloromethane, tetrahydrofuran, dimethoxyethane, or acetone.
Another reaction mixture within the invention includes a functionalized allylic olefin substrate; a ruthenium-based catalyst capable of catalyzing the metathesis condensation of the functionalized allylic olefin substrate; a functionalized olefin product having a different chemical structure than the functionalized allylic olefin substrate, the product being formed by the metathesis condensation of the substrate; and a solvent, the solvent having dissolved therein the substrate and the catalyst. In this reaction mixture, the catalyst can be 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium benzylidene (Ru*); and the functionalized allylic olefin substrate can be allyl alcohol or allyl cyanide. Where the functionalized allylic olefin substrate is allyl alcohol, the functionalized allylic olefin product can be 2-butene-1,4-diol. And where the functionalized allylic olefin substrate is allyl cyanide, the functionalized allylic olefin product can be 1,4-dicyanobutene.
Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In the case of conflict, the present specification, including any definitions will control. In addition, the particular embodiments discussed below are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.